Bioconversions of ferulic acid and p-coumaric acid to volatile phenols by aspergillus spp. and bacteria found in soy sauce koji and mashes

Abstract

Bioconversions of ferulic acid and p-coumaric acid to volatile phenols (VPs) such as 4-ethylguaiacol (4EG), which is a characteristic flavor of soy sauce, by Aspergillus spp. and bacteria found in soy sauce koji and mashes were examined in the presence of sodium chloride. Aspergillus oryzae and A. sojae, Pediococcus halophilus, and Micrococcus spp., which were isolated from soy sauce koji and mashes did not produce VPs from ferulic acid or p-coumaric acid. However, Bacillus strains such as B. subtilis, B. licheniformis, and B. megaterium, which are recognized as spoilage bacteria in soy sauce making, produced vinyl phenols, when the cell number was more than 107 cells/ml. A strain isolated from soy sauce koji in this study, a Staphylococcus sp., which grew in high salt medium such as 20% NaCl and/or in higher pH media than that of soy sauce such as pH 5.5, produced vinyl phenols. The results suggest that elimination of the various spoilage bacteria such as B. subtilis and Staphylococcus spp. in soy sauce making is needed for keeping the best quality of soy sauce, especially good flavor.